Method for packaging an integrated circuit

ABSTRACT

The present invention provides a modular electronic component (10) wherein a sequence of leads (26) of a lead frame (12) differs from a sequence of bonding pads (16) on an integrated circuit (14). When lead frame (12) is placed adjacent integrated circuit (14), first and second power buses (22) and (24) are disposed on a first side (18) of bonding pads (16). First portion (30) of leads (26) and lead finger (28) are disposed on second side (20) of bonding pads (16). Bonding members (42) couple appropriate bonding pads (16) with corresponding leads (26), first and second power buses (22) and (24), and lead finger (28). In this manner, the pin out of modular electronic component (10) may be altered by incorporating appropriate lead fingers (28) without changing the sequence of bonding pads (16).

TECHNICAL FIELD OF THE INVENTION

This invention relates in general to the field of electronic devices,and more particularly to a method and apparatus for packaging anintegrated circuit.

BACKGROUND OF THE INVENTION

Many modern electronic systems incorporate various modular electroniccomponents. For example, personal computers may comprise modularelectronic components in the form of Dynamic Random Access Memory units.Each of the modular electronic components may comprise an integratedcircuit fabricated on a semiconductor substrate. Each modular electroniccomponent is coupled to the electronic system by a series of pinsextending in a predetermined sequence from a body of the modularelectronic component. The pins are coupled to leads of a lead frame. Thelead frame is coupled to the integrated circuit during the fabricationof the modular electronic component.

A specific electronic signal may be associated with each pin of themodular electronic component. When the modular electronic component isproperly coupled to the electronic system, the pins transmit theseelectronic signals between the integrated circuit and correspondinglines of the electronic system. Thereby, the electronic system mayfunction properly. If, however, the sequence of pins of the modularelectronic component does not match a sequence of corresponding lines ofthe electronic system, the electronic system will not receive the propersignals at the proper lines. Therefore, the electronic system would notfunction properly.

One typical method for connecting the lead frame to the integratedcircuit is referred to in the industry as lead frame-over-chip (LOC)technology. As mentioned above, the integrated circuit is typicallyfabricated on a semiconductor substrate. The integrated circuit andsubstrate is commonly known as an "integrated circuit chip." Theintegrated circuit also comprises a row of bonding pads for connectingthe integrated circuit to the leads of the lead frame. According to LOCtechnology, the lead frame is placed over the integrated circuit chipsuch that the row of bonding pads may be coupled to appropriate leads ofthe lead frame.

Typically, the leads of a lead frame may be routed in only 2 dimensions.This means that leads may not cross over other leads. Consequently, thesequence of leads in a lead frame will be the same as the sequence ofthe bonding pads on the integrated circuit. Integrated circuits aremanufactured by a number of different companies. Often, each of thesecompanies produce competing integrated circuits that perform the samefunction. However, the various integrated circuits differ in the mannerin which the integrated circuits are organized on the semiconductorsubstrate. For example, because integrated circuits are complicated anddesigned independently by these companies, the sequence of bonding padsmay vary from manufacturer to manufacturer even though the integratedcircuits perform the same function. Therefore, each modular componentproduced by a particular manufacturer may have a different "pin out." A"pin out" is the physical sequence in which pins associated withspecific electronic signals extend from the modular electroniccomponent.

Two modular components that perform the same function but have differentpin outs will not both function properly when coupled to a specificelectronic system. At least one of the modular components will notprovide the appropriate electronic signals to the system. This iscontrary to the interchangeability that modular components shouldprovide. A prior solution involves adding a few semiconductor processingoperations to change the sequence of bonding pads of an existingintegrated circuit design. In this manner, the bonding pads may beformed in the same sequence as the leads of the lead frame.

SUMMARY OF THE INVENTION

In accordance with the present invention, a method and apparatus forpackaging integrated circuits is provided which substantially eliminatesor reduces disadvantages and problems associated with prior methods.More specifically, the present invention provides a lead frame for usewith packaging an integrated circuit having a plurality of bonding padsforming a row. The lead frame comprises first and second power buses, aplurality of leads, and at least one lead finger. The first and secondpower buses are parallel along a portion of the power buses. When thelead frame is placed adjacent to the integrated circuit, the parallelportion of the power buses is disposed adjacent to a first side of therow of bonding pads such that the power buses are parallel to thebonding pads. Additionally, when the lead frame is placed adjacent tothe integrated circuit, the leads are disposed adjacent to a second sideof the row of bonding pads. The lead finger is coupled to an end portionof one of the leads. Each of the leads and the lead fingers are adjacentto an appropriate bonding pad. The leads extend away from the row ofbonding pads and are operable to couple the integrated circuit to anexternal system.

A technical advantage of the present invention inheres in the fact thatit provides a lead frame wherein the sequence of leads extending fromthe lead frame may be different from the sequence of correspondingbonding pads of the integrated circuit. Thereby, the present inventionallows a modular electronic component to be fabricated to have variouspin outs even though the bonding pads are not in the same sequence asthe leads. In this manner, a manufacturer of a particular integratedcircuit may match the pin out of another manufacturer of a similarintegrated circuit by simply varying the lead frame.

Another technical advantage of the present invention inheres in the factthat it allows a manufacturer of an integrated circuit to improve thedesign and layout of the integrated circuit without interfering with theability of the manufacturer to meet a pin out requirement that isstandard to the industry.

Another technical advantage of the present invention inheres to the factthat it allows various manufacturers of similar integrated circuits toprovide their devices to the consumer with a common pin out.

Another technical advantage of the present invention inheres in the factthat it allows a manufacturer to inexpensively modify the pin out of amodular electronic component. By implementing the teachings of thepresent invention, the pin out can be changed without redesigning theunderlying integrated circuit to change the sequence of the bondingpads.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptiontaken in conjunction with the accompanying drawings in which likereference numbers indicate like features and wherein:

FIG. 1 is a schematic diagram of a lead frame constructed according tothe teachings of the present invention for use with a 16 megabyte by 8Dynamic Random Access Memory (DRAM) in a vertical package; and

FIG. 2 is a schematic diagram of a lead frame constructed according tothe teachings of the present invention for use with a 16 megabyte by 9DRAM in a vertical package.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic diagram of a modular electronic componentindicated generally at 10 and constructed according to the teachings ofthe present invention. Modular electronic component 10 comprises a leadframe 12 and an integrated circuit 14.

Integrated circuit 14 may comprise, for example, a Dynamic Random AccessMemory (DRAM), or other suitable integrated circuit. In this embodiment,integrated circuit 14 comprises a 16 megabyte by 8 DRAM. Integratedcircuit 14 comprises a row of bonding pads 16 spaced along a length ofintegrated circuit 14. Bonding pad 16 have first and second sides 18 and20. In order to simplify the schematic diagram to better illustrate theteachings of the present invention, various details of integratedcircuit 14 are not shown in FIG. 1.

Lead frame 12 comprises first bus 22, second bus 24, a plurality ofleads 26, a lead finger 28 and pins 29. Leads 26 have first and secondportions 30 and 32. When lead frame 12 is placed adjacent integratedcircuit 14, first portion 30 of leads 26 is disposed adjacent to secondside 20 of bonding pads 16. In this manner, leads 26 extend away fromsecond side 20 of bonding pads 16 toward side 34 of integrated circuit14. Pins 29 are coupled to second portion 32 of leads 26. Pins 29 areoperable to couple modular electronic component 10 to an electronicsystem (not shown) by using a surface mount technology, or othersuitable conventional mounting technology. Pins 29 may comprise, forexample, 32 pins as shown in FIG. 1, or other appropriate number ofpins, as required by a specific integrated circuit 14.

Lead finger 28 comprises first and second portions 36 and 38. Firstportion 36 of lead finger 28 is coupled to a first portion 30 of lead26b. In this manner, second portion 38 of lead finger 28 is deposedadjacent an appropriate bonding pad 16. Additionally, lead finger 28 issubstantially parallel to bonding pads 16 when lead frame 12 is placedadjacent integrated circuit Alternatively, lead frame 12 may comprisemore than one lead finger 28 to allow for proper coupling of bondingpads 16 to leads 26. In this manner, modular electronic component 10 maybe provided with a sequence of pins 29 different from a sequence ofbonding pads 16 of integrated circuit 14.

First and second power buses 22 and 24 are substantially parallel alonga portion 40 of first and second power buses 22 and 24. First and secondpower buses 22 and 24 may be coupled to appropriate pins 29 to providepower to integrated circuit 14. When lead frame 12 is placed adjacent tointegrated circuit 14, portion 40 of first and second power buses 22 and24 is disposed adjacent first side 18 of bonding pads 16.

Finally, bonding members 42 couple bonding pads 16 with first power bus22, second power bus 24, leads 26, and lead finger 28. Bonding members42 may be fabricated to couple a bonding pad 16 to first power bus 22even though second power bus 24 is located between first power bus 22and bonding pad 16. This is known in the industry as "boding over"a bus.Bonding member 42 actually forms an arc shape. This allows bondingmember 42 to cross over second bus 24 without contacting second bus 24.

Modular electronic component 10 may be fabricated by first placing leadframe 12 adjacent integrated circuit 14. First and second power buses 22and 24 of lead frame 12 are disposed adjacent first side 18 of bondingpads 16 along portion 40 of first and second power buses 22 and 24.Additionally, first portion 30 of leads 26 are disposed adjacent secondside 20 of bonding pad 16. Finally, lead finger 28 is disposed alongsecond side 20 of bonding pads 16 such that lead finger 28 issubstantially parallel to bonding pads 16. With the lead frame in place,bonding pads 16 are coupled to first portion 30 of leads 26 and secondportion 38 of lead finger 28 by bonding members 42. Bonding members 42may be fabricated, for example, by a conventional ball and stitchbonding technique. Finally, modular electronic component 10 is encasedin a housing (not shown) according to a conventional technique. Forexample, modular electronic component 10 may be exposed to a slurry ofplastic particles and other appropriate constituents in a conventionalmolding technique.

As discussed previously, the sequence of bonding pads 16 in anintegrated circuit 14 generally is the same as the sequence of leads 26and corresponding pins 29. The present invention allows the sequence ofleads 26 to be different from the sequence of bonding pads 16 of anintegrated circuit 14 while still coupling appropriate leads 26 toappropriate bonding pads 16.

In the embodiment of FIG. 1, lead 26a and bonding pad 16b are associatedwith the signal WE₁₃ . Additionally, lead 26b and bonding pad 16a areassociated with signal OE₁₃ . As shown in FIG. 1 bonding pads 16a and16b are not fabricated in the same sequence as leads 26a and 26b.However, by constructing lead frame 12 according to the teachings of thepresent invention, lead 26a may be coupled to bonding pad 16b while lead26b may be coupled to bonding pad 16a. Bonding pad 16b may be coupled tolead 26a by "bonding over" the single lead finger 28. Bonding pad 16amay be coupled to lead 26b by a bonding member 42 coupling bonding pad16a to adjacent lead finger 28. In this manner, the pin out of modularelectronic component 10 may be modified without changing the sequence ofbonding pads 16 on integrated circuit 14.

In FIG. 2, integrated circuit 14 is a 16 megabyte by 9 DRAM. In thisembodiment, two leadfingers 28a and 28b are incorporated because twopair of bonding pads 16 are out of order. In this embodiment, lead 26cand bonding pad 16d are associated with the signal DQ8. Lead 26d andbonding pad 16c are associated with the signal CAS₁₃ . Lead 26e andbonding pad 16f are associated with the signal WE₁₃ . Finally, lead 26fand bonding pad 16e are associated with signal OE₁₃ . As shown in FIG. 2bonding pads 16c through 16f are not fabricated in the same sequence asleads 26c through 26f. However, by constructing lead frame 12 accordingto the teachings of the present invention, lead 26c may be coupled tobonding pad 16d while lead 26d may be coupled to bonding pad 16c.Furthermore, lead 26e may be coupled to bonding pad 16f while lead 26fmay be coupled to bonding pad 16e. Bonding pads 16c and 16f may becoupled to leads 26d and 26e respectively by "bonding over" single leadfingers 28a and 28b. Bonding pads 16d and 16e may be coupled to leads26c and 26f via adjacent lead fingers 28a and 28b. In this manner, thepin out of modular electronic component 10 may be modified withoutchanging the sequence of bonding pads 16 on integrated circuit 14.

Although the present invention has been described in detail, it shouldbe understood that various changes, substitutions and alterations can bemade hereto without departing from the spirit and scope of the inventionas defined by the appended claims. For example, the teachings of thepresent invention are applicable to zig-zag in-line packaging as well asvertical packaging.

What is claimed is:
 1. A method for packaging an integrated circuithaving a row of bonding pads, the method comprising the steps of:forminga lead frame including first and second power busses mutually parallelalong a portion of said busses, a plurality of leads having first andsecond ends, and at least one lead finger having first and second ends;placing the lead frame adjacent the integrated circuit such that theportion of the first and second power buses is disposed adjacent a firstside of the row of bonding pads, parallel to the bonding pads, thesecond end of the leads are disposed adjacent a second side of the rowof bonding pads, and each of the leads and the lead fingers are adjacentan appropriate bonding pad.
 2. The method of claim 1, and wherein thestep of forming a lead frame comprises the steps of:forming first andsecond power buses, the first power bus being formed parallel to thesecond power bus along a portion of the power buses; forming a pluralityof leads having first and second ends, the first end operable to couplethe integrated circuit to an external system; and forming at least onelead finger having first and second ends, the first end coupled to thesecond end of one of the leads.
 3. The method of claim 1, furthercomprising the step of forming bonding members to couple selectedbonding pads to appropriate leads, the lead fingers, and the first andsecond power buses.
 4. The method of claim 1, and further comprising thestep of forming a plastic encasement for the integrated circuit byexposing the integrated circuit and the lead frame to a slurry ofplastic particles in an appropriate mold.
 5. The method of claim 1, andfurther comprising the step of forming bonding members according to aball and stitch method to couple the leads, the lead fingers, and firstand second power buses.